Safety device for electrical circuits



Nov. I, 1927. 1,647,282 0. DREYER SAFETY DEVICE FOR ELECTRICAL CIRCUITS Filed y 1925 INVENTOR. Otto fircy BY @ZQW ATTORNEY Patented Nov. 1,1927.

UNITED STATES OTTO DREYEB, OI. ESSEN-ON-THE-RUHR, GERMANY.

SAFETY DEVICE FOR ELECTRICAL CIRCUITS.

Application filed Kay 7, 1925, Serial No. 28,724, and in Germany February 12, 1925.

The present invention relates to a safety device for electrical circuits comprising in addition to an exchangeable fuse a likewise exchangeable thermal releasing unit which depends upon the thermal condition of the circuit to be protected and which when a predetermined temperature is exceeded so increases the current flowing through the fuse that the latter is melted or blown and the endangered circuit thereby cut out.

The primary object of the invention is to simplify and facilitate the construction of the safety device and reduce the amount of attention required to keep the same in working order. At the same time the invention has in view so to arrange the safety device that there can be no danger to the circuit to be protected owing to the said device having been attended to carelessly or incorrectly.

marily consists in the fuse being so mechanically coupled with the thermal releasing unit arranged axially behind it that the releasing unit can be inserted into and withdrawn from the device by the aid of the fuse.

A further essential featureof the invention is that the thermal releasing unit carries or forms simultaneously the abutment contact as well as the pass-rin or fitting ring for the foot-contact of the %use, so that, on the one hand, should a fuse without thermal releasing unit be inserted the former has no electrically conductive connection at its footcontact, while at the same time insertion of a fuse intended for a higher fusing current than prescribed isprevented. Finally the invention consists in this, that the thermal releasing unit is in such a manner non-interchangeable, according to the releasing temperature or current, in the part ormember receiving it, (for instance, in the central tube of a heating coil), that a releasing unit of Higher fusing temperature than allowable for the circuit to be protected cannot be inserted.

One practical embodiment of the invention is shown by way of example in the'ac companying drawing wherein:

Figs. 1 and 2 are two axial sections of the safety device, the switching or contact pin of the thermal releasing unit being shown in its normal position in Fig. 1 and in its contacting position in Fig. 2.

The essence of the present invention prithe line 3--3 in terial. The heating coil 17 is as usual wound on a metal tube 22 which serves for receiving the thermal releasing unit. The winding of the coil 17 is conductively connected at its inner end to the metal tube 22 and at its outer end to a lateral terminal 72. Said.

winding is so designed, as is known, that 1t becomes heated up exactly in correspondence as far as this is possible with the circultto be protected. The nature'and purpose of the insulating ring 71 are hereinafter further explained more in detail. Above the insulating rin 71 there is secured in an enlargement of ta recess 70 the threaded ring 7? into which the head or plu 9 of the devlce provided with a threa ed tube 8 is screwed and which is conductively connected to a second lateral terminal 74. The heatingcoil 17 and insulatin ring 71 have a somewhat larger external diameter than the threaded ring 73 so that they are protected by the latter from unauthorized withdrawal and exchange. The space between the insulating ring 71 and the head 9 of the device serves for the reception of an ordinary fuse, which in the embodiment shown is a Diazed cartridge 10. This at its head contact is conductively connected to the threaded tube 8 while at its foot it is connected to the central tube 22 of the heating coil 17 by means of the thermal releasing unit now to be described.

The thermal releasin unit consists of a metal casing or guide tu e 30 mounted in the central tube 22 of the heating coil and havin therein just sufficient play to enable it to e readily pushed in and pulled out. The casing 30 has a metal flange 75 which bears on the upper flange of the metal tube 22 of the heating coil 17 and thereby ensures good contact with this tube. Displaceably mounted in the casing 30 is a contact pin 31 which is acted u on by a spring 32 pressing it downwardly ut which is normally securely soldered in its upper extreme POSI- tion shown in Fig. 1. In order to prevent the pin 31 from being completely pushed out of the casing 30, the lower edge of the latter on the one hand is bent inwardly and the pin 31 on the other hand is provided at its upper end with a collar 76. This collar 1s provided with an annular groove or channel 7 7 for the reception of the soldering metal, whereby the loss of the latter is prevented.

That portion 78 of the guide tube 30 which projects upwardly from the heating coil 17 is formed as an inwardly resilient clamping sleeve by being provided with a number of longitudinal slits or slots, the inside diameter of this sleeve corresponding with the diameter of the pass-pin. or fitting pin 10 of the fuse 10. The fuse when in place engages by means of its pin 10 in the clamping sleeve 78 which firmly clasps the pin in conse uence of the resiliency of its wall. The use and thermal releasing unit are thereby so coupled together that when the fuse is removed the releasing unit is simultaneously withdrawn from the device. Moreover the clamping sleeve 78 electrically connects the fuse to the thermal releasing unit so that a separate contact screw is not required. The clamping sleeve 78 has a different inside diameter according to the desired fusing current of the fuse 10, the diameter in Figs. 1 to 3 being suitable for a cartridge of 6 amperes fusing current, while in the case of the releasing units according to Figs. 4 and 5 the clamping sleeve is arranged for the reception of the fitting pin of a cartridge of 10 and 25 amperes respectively. Since in the two latter cases the outer end 78 of the guide tube 30 which serves as clamping sleeve and pass-ring or fitting ring has a larger diameter than that portion of said tube 30 which is mounted in the central tube of the heating coil, there is formed on the guide tube a shoulder which is capable of serving as both stop and contact face, so that in the case of the releasing units according to Figs. 4 and 5 the special flange 75 is dispensed with. Obviously the devicemay be designed not only for 6, 10 and 25 amperes but also for all practical current values.

The portion of the guide tube 30 which contains the contact pin 31 and the spring 32 is open at top and when the fuse 10 is inserted, the loadin spring 32 of the contact pin 31 is stresse or tensioned by the said fuse. In the embodiment shown, the contact pin 31 serves to bring about a short circuit between the two poles of the circuit to be protected and thereby to blow the fuse 10.

the circuit to be protected. The current then flows from the terminal 74 through the fuse 10, the thermal releasing unit 30, 31 and the heating coil 17, to the terminal 72. The

third terminal 34 is connected to the second lead of the circuit to be protected. When the circuit to be protected is normally loaded the contact pin 31 is located in its upper extreme position shown in Fig. 1 so that no conductive connection exists between it and the contact 33. When in consequence of the circuit being overloaded excessive or unallowable heating occurs the pin 31 is unsoldered by the heating coil 17 which becomes heated in correspondence with the heating of the circuit, whereupon the spring 32 pushes the pin 31 downwards against the contact 33. There is thus produced behind the fuse 10 a short circuit between the two poles of the circuit, the consequence of which is that the endangered circuit is cut out by the fuse 10. In order again to give the initial setting to the protective device the head 9 of the latter is unscrewed, whereupon the fuse 10 together with the thermal releasing unit may be removed by a simple manipulation. When this has been done, the thermal releasing unit 3031 will have been withdrawn as a unit from the fuse nd the contact pin 31 may then be moved ack into its initial position in the tube 30 and resoldered therein. Thereupon the renovated releasing unit is applied to a new fuse and together with the latter inserted into the protective device and secured by screwing up the head 9. The device is then again ready for operation.

Besides acting in the event of excessive heating the protective device may obviously act in the event of sudden heavy overloads without the thermal releasing unit coming into action. In this case the circuit is cut out directly by the fuse 10 and only the latter need then be exchanged. The condition of the fuse 10 is as usual observable on an inspection plate visible in the inspection hole 41 of the head 9 of the device, said fuse being provided in practice with the usual colored markers or indication plates which, on the melting of the wire, drop off and thus indicate that the fuse has blown, while the condition of the thermal releasing unit is observable from the position of the contact pin 31 after said unit together with the fuse has been withdrawn from the device. If this pin does not project from the casing 30 then only the fuse has acted.

In order to prevent a thermal releasing unit for a higher releasing temperature or current being inserted instead of the releasing device prescribed for the circuit the guide tube 30 of the contact pin and with this, of course, also the central tube 22 of the heating coil are preferabl diameter, a large diameter (Fig. 5) corresponding to a high, and a small-diameter (Figs. 1-4) to a low, releasing temperature. There can thus, it is true, be inserted into the device a releasing unit for a lower releasing temperature but never a releasing unit for a higher temperature.

Moreover, in order to prevent the insertion into the device of a releasing unit which indeed is correct for the prescribed releasing temperature but has a pass-ring or fitting ring for a fuse of higher fusing current than for the circuit to be protected the above described insulating ring'71 is provided. In Figs. 1 to 3 this ring has an inside diameter corresponding to the outside diameter of the flange 75 provided on the thermal releasing unit, and in a releasing unit according to Fig. 4 or 5 an inside diameter corres onding to the outside diameter of the c am ingsleeve 78 or the shoulder 7 5, so that t ere can be inserted instead of the prescribed releasing unit certainly a releasing unit having a smaller clamping sleeve but never a releasing unit having a larger one. The insulating ring 71 further serves to prevent the circuit being closed in the absence of the thermal releasing unit. To this end the ring has a greater height than the length of the pin 10 of the fuse 10 so that the foot-contact of the latter cannot come directly into contact with the central tube 22 of the heating coil 17. There is thus no conductive con-.

nection between the fuse 10 and the heating coil 17 when a fuse without a thermal releasing unit is inserted.

Obviously many modifications of the embodiment illustrated, as also other embodiments falling within the scope of the appended claims, are possible. For example,

' the type of coupling between the thermal releasing device and the central tube 22 of the heating coil 17 may be other than that shown and modified as desired within the range of equivalents. For securely soldering the contact pin 31 in the casing 30 any suitable mineral or non-mineral fusible substance may be used and there might be employed,

graded in 7 comprising, in combination, a heating coil, an exchangeable fuse, and an exchangeable thermal'releasing device disposed between the coil and the fuse and controlling the passage of the current through the fuse, said fuse and said thermal releasing unit being mechanically coupled so as to adapt the releasing unit to be inserted into and with drawn from the device by and with the fuse; 2. A safety device according to claim 1 characterized by the thermal releasing unit having a resilient slip-joint connection with a pin-like projection 10" on the fuse and forming simultaneously the abutment contact and fitting ring for the foot-contact of the fuse.

3. A safety device in a combination a'ccording to claim 1, characterized in that the thermal releasing unit and the part receiving it are so constructed that the receiving part is adapted to receive only a releasing unit of a predetermined maximum size and operative at a predetermined maximum releasing temperature.

4. A safety device according to claim 1, characterized by the outer end of the thermal releasing unit formed as a resilient I characterized by a thermal releasing device which can be pushed in and pulled from the central tube of the heating coil, the inward movement of said device being limited' a stop, which simultaneously brings b about electric conductive connection betweenthe releasing unit and the heating coil.

7. A safet device according toclaim 1, characterize by the feature that a guide casing is provided for the thermal releasing unit, which casing contains a displaceable but normally securely soldered contact pin and is open in the direction of the clamping sleeve (as 78), and that the spring (as 32) which influences the contact pin is so arranged that it is compressed and placed under tension by the fuse.

8. A safety device according to claim 1, characterized in that the thermal releasing device has a clamping sleeve (as 78) surrounded by an insulating ring (as 71) the inside diameter of which is so dimensloned that insertion of a thermal releasing unit leigving a larger clamping sleeve is preventi). A safety device according to claim 1,

device has a clampin being graded accordin to the releasing temperature by change 0 the diameter of the central tube as 22) of the heating coil and of that part (as 30) of the exchangeable releasing unit which is inserted therein.

11. A safety device accordin to claim 1, characterized by the heating coil 17 and insulatlng ring 71 having a somewhat greater outside diameter than the threaded ring as 73) into which the head of the safety device is screwed and being so secured by the latter from unauthorized withdrawal.

In testimony whereof I aflix my signature.

- oT'ro DREYER. 

